Research Of Microscopic Mechanism Of Shale Gas Adsorption In Nano-pores Of Mud Shale

Studying the adsorption properity of shale gas plays an extremely important role in shale gas mining.The shale gas is mainly stored in the nanopores of the shale.The adsorption properity of the shale gas depends mainly on its adsorption behavior in the nanopores of the shale.In this paper,molecular dynamics and Monte Carlo method were used to simulate the adsorption behavior of shale gas in nanopores,and the physical relationship between shale gas adsorption performance and various influencing factors was analyzed.According to the main components of shale reservoirs,nanoporous models of organic matter,quartz and clay minerals were established,and shale gas adsorption molecular simulations under various conditions were carried out by using different temperatures,pressures and pore sizes.The effects of gas pressure,ambient temperature and pore size on the adsorption capacity of shale gas were studied,and the dependence of shale gas adsorption capacity on the organic matter and mineral composition of shale was discussed.The molecular calculation results show that:(1)Influenced by the molecular potential energy of the pore wall surface,the methane molecules are approximately parallel to the pore wall in the range of 0.5 nm,showing an adsorption state;while the distribution away from the pore wall is relatively dispersed,the methane molecules are less affected by the pore wall surface,showing a free state.(2)The amount of methane adsorption in the organic matter,quartz and clay minerals Nano-pores increases with the increase of pressure,and the physical relationship between them can be described by a power function.The adsorption ratio of methane in the Nano-pore gradually decreases with the increase of pressure.(3)When the pressure and temperature are the same,the amount of methane adsorption in the organic matter,quartz and clay minerals Nano-pores increases linearly with the increase of pore size.(4)When the pressure and the aperture are the same,The amount of methane adsorption in the organic matter,quartz and clay minerals Nano-pores of decreases linearly with the increase of temperature.(5)Under the same pressure,temperature and pore size,the shale gas adsorption capacity of the organic nanopores is larger than that of the clay mineral nanopores and the shale gas adsorption of the clay mineral nanopores is larger than that of the quartz nanopores.The shale gas adsorption of the montmorillonite nanopores is larger than illite and kaolinite.The adsorption heat of organic matter is greater than that of clay minerals and quartz.The order of adsorption capacity of shale gas in several shale materials is: organic matter > montmorillonite > illite > quartz > kaolinite.